This invention relates generally to oil well cementing compositions and specifically to an additive for such compositions and method of making the same for controlling fluid loss during cementing operations.
Cement compositions are used in the oil and gas industry to cement the annular space in the well bore between the surrounding formation and pipe or casing. In a typical operation, the cement slurry is pumped down the inside of the casing and back up the outside of the casing through the annular space. The amount of water which is used in forming the cement slurry will vary depending upon the type of hydraulic cement selected and the job conditions at hand. The amount of water used can vary over a wide range dependent in large measure upon the consistency of the slurry required and upon the strength requirement for the particular job. In many cases, the hydraulic cement must be placed within or next to a porous medium, for example, the earthern strata in the well bore. When this happens, the water tends to filter out of the slurry and into the strata during the setting of the cement. Many difficulties are attendant with uncontrolled fluid loss of this type such as uncontrolled setting rate, improper placement of the slurry, impaired strength properties, and contamination of the surrounding strata. These conditions are all undesirable in oil and gas well cementing operations.
In order to lessen the loss of fluid from the aqueous cement slurry, various materials have been employed in the past. The use of polyamine compounds selected from the class consisting of polyalkylenimines, polyalkylenepolyamines and mixtures thereof is taught in U.S. Pat. No. 3,491,049 to Gibson et al, issued Jan. 20, 1970. However, polyamines do not generally function as fluid loss additives when used alone but must be synergized with a companion material, typically one of the so-called "dispersant" materials. In the 3,491,049 patent, a sulfonated naphthalene condensate dispersant is used as an additional additive to the cement slurry which cooperates with the polyamine additive to provide satisfactory fluid loss in cement slurries used at about 200.degree. F. and below. The sulfonated polymer dispersants are typically low molecular weight materials, e.g., in the range of about 1,000 to 3,000.
Sulfonated polystyrene has also been used in the past as a fluid loss additive for cement compositions. Thus, U.S. Pat. No. 3,234,154 to Martin, issued Feb. 8, 1966, teaches the use of a sulfonated polystyrene polymer having a molecular weight in the range of 300,000 to 4,000,000. The sulfonated polystyrene is used in conjunction with a lignin amine derivitive. The use of a polyamine is not taught.
U.S. Pat. No. 3,511,314 to Scott, Jr., et al, issued May 12, 1970, teaches the use of the reaction product of a polyamine and "an acidic compound selected from the class consisting of carboxylic acids, sulfonic acids, polymers having a carboxyl substituent, and polymers having a sulfonate substituent" as fluid loss additives for cement slurries. The acid component is once again identified as the condensation product of a mononaphthalene sulfonic acid and formaldehyde. The condensation product is thus a low molecular weight dispersant type compound, i.e., in the range of 1,000 to 3,000. The use of a high molecular sulfonated polymer is not taught. The fluid loss additive is used in the examples in the temperature range of 200.degree. F. and below.